1. Field of the Invention
This invention relates to a device for the administration by inhalation of a medicament in dry powder form, which comprises a medicament reservoir and medicament metering means including a metering chamber communicable with the reservoir.
2. Description of the Prior Art
Devices for the administration by inhalation of medicaments in dry powder form are well known. European Patent Application No 166294 discloses such a device comprising a medicament reservoir and a metering chamber with a volume chosen such that, when filled, the chamber contains the desired weight of medicament for a dose. Filling of the metering chamber is accomplished under the influence of gravity, the chamber being located at the bottom of the reservoir. This passive method of charging the metering chamber suffers from the disadvantage that variations in the density of the metered powder can easily occur resulting in inaccurate or inconsistent dosing. The packing density of the powder may also depend on the weight of powder remaining in the reservoir, leading to a gradual reduction in the dose delivered by the device. In addition, the dose metered is strongly dependent on the orientation of the device.